DESCRIPTION (Applicant's abstract): The proposed research will use recently developed maps of regional activity patterns associated with behaviors that do and do not entail explicit learning, to test the hypothesis that proteolytic and synthetic chemistries linked to long term potentiation (LTP) are activated in situ during learning. Behavioral groups include rats at different stages in olfactory discrimination learning, recently engaged in copulation, or having received an IP saline injection; analysis will focus on subfields of hippocampus and amygdala. The first aim is to map cfos mRNA expression to identify regions activated during learning: the analysis will complete the evaluation of cfos expression in 8 behavioral groups. The second aim is to test the hypothesis that mRNA expression for the cytoskeleton-associated protein Arc increases in regions activated during behavior and that this effect will be greater in conditions associated with explicit learning as compared to conditions that are not. In addition, effects on Arc protein content will be evaluated. The third aim is to test the hypothesis that neurotrophin mRNA expression covaries with neuronal activity in a subset of areas that exhibit changes in c-fos expression, and most particularly in areas activated with learning as opposed to familiar behaviors. The fourth aim is to use antisera specific for spectrin fragments deriving from calpain activity to test the hypothesis that the protease is stimulated in dendritic spines in association with LTP and in select hippocampal and amygdala areas during learning. The chemistries to be evaluated (calpain activity, neurotrophin and Arc expression) are argued to be critical for certain forms of synaptic plasticity, and are candidates for involvement in memory encoding. The proposed work will provide a first test for their presence in regions engaged learning behaviors.